Disconnect switch having reduced susceptibility to electrical breakdown

ABSTRACT

A grading post is provided at the jaw of a disconnect switch, and both it and the cooperating contact blade of the switch are constructed with substantially spherical projections in offset alignment at their respective ends to reduce the effect of corona and radio interference.

United States Patent 0 Joseph A. Turgeon Toronto, Ontario, Canada June 15, 1970 Aug. 31, 1971 I-T-E Circuit Breaker (Canada) Limited Port Credit, Ontario, Canada Inventor Appl. No. Filed Patented Assignee DISCONNECT SWITCII HAVING REDUCED SUSCEPTIBILITY T0 ELECTRICAL BREAKDOWN 5 Claims, 1 Drawing Fig.

US. Cl 200/48,

317/77 Int. Cl. .l H0lh 31/00 Field of Search... 200/48 R,

' 48 RP, 48 V, 48 SB, 48 CB; 317/77 [56] References Cited UNITED STATES PATENTS 3,530,265 9/1970 Albright 200/48 Primary Examiner Robert K. Schaefer Assistant Examiner-H. J Hohauser Attorney0strolenk, Faber, Gerb and Soffen ABSTRACT: A grading post is provided at the jaw of a disconnect switch, and both it and the cooperating contact blade of the switch are constructed with substantially spherical projections in offset alignment at their respective ends to reduce the effect of corona and radio interference.

DISCONNECT SWITCH HAVING REDUCED SUSCEPTIBILI'IY TO ELECTRICAL BREAKDOWN This invention relates to electrical switching devices and, more particularly, to an improved disconnect switch having reduced susceptibility to electrical breakdown, corona and radio interference.

Disconnect switches conventionally include an insulatormounted contact jaw having two spaced contact members, and disconnect blade which is pivotally mounted by a hinged bearing on an insulator to spring into the contact jaw and thus electrically connect with the contact members. The blade is also rotatable about its longitudinal axis within the hinged bearing so that the blade may be moved, edge first, between the contact members of the jaw and then be rotated about its axis so that contact edges of the blade meet the jaw members. The blade is thus securely wedged and gripped within the jaw in high pressure electrical engagement.

The instant invention is directed toward providing an improved disconnect switch for use in extra high voltage environments, where typical voltages and currents are of the order of 700 kv. with load currents of 3000 amperes and higher. In these environments, the possibilities of electrical breakdown, corona discharge, and radio interference are more pronounced than at lower operating voltages.

As will become clear hereinafter, a disconnect switch embodying the invention incorporates a grading post at the jaw contact assembly, with both the grading post and the cooperating contact blade of the switch having substantially spherical projections located at their respective ends. As will also become clear, these projections are offset (i.e., not coaxial) with respect to theirgrading post and blade support members and, furthermore, are offset away from one another so that their separation is never less than that between the contact blade and the grading post when correspondingly oriented in a vertical (e.g. 90) position. Disconnect switches constructed according to the invention are particularly useful in isolating electrical apparatus and portions of electrical systems from extra high voltage lines for the safe handling, maintenance and repair, and inspection they require.

It is therefore seen that a first object of the invention is to provide a novel disconnect switch which serves to reduce a concentrated build up of an electric field which may tend to cause electrical breakdown.

It is another object of the invention to provide such a disconnect switch wherein the possibility of corona discharge and the effects of radio interference at extra high voltage are substantially reduced.

These, as well as other, objects of the instant invention will become apparent when considering the following description taken in connection with the single FIGURE of the drawing which shows a front elevation view of a disconnect switch constructed in accordance with the present invention.

The disconnect switch 100 is shown in its closed position, and includes three insulator support stacks l0, l2 and 14 which stand in a row. The switch assembly extends upward from the ground surface I6, as by support structures 18 and 20, respectively. A cross member or frame 22 is connected between the upper ends of the structures 18, 20, with the insulator stacks l2 and 14 extending upwardly therefrom being stationary. Insulator support 10, which also extends upwardly from cross member 22, on the other hand, is rotatable. The disconnect switch 100 may be of the type shown in US. Pat. No. 2,673,902, issued March 30, 1954, and is designed to carry current from bus 26 to bus 28 (shown schematically) when in closed position and to interrupt current flow when opened.

The disconnect switch 100 also includes an elongated contact blade 30, which is typically mounted at one end to a rotatable hinged support 32 at the upper end of insulator support stacks l0, 12. The opposite, or contact end, 34 of the disconnect switch blade 30 engages a cooperating stationary contact jaw 36 when in the closed position (as shown in the solid lines of the drawing), with the jaw 36 being mounted at the upper end of insulator stack 14.

Opening of the disconnect switch to move its elongated contact blade 30 to the position shown dotted as 30' is-provided by the rotation of a crank wheel 38, either manually or by a motor driven assembly shown generally as 40. This, in turn, rotates transmission shaft 42 which rotates insulator stack 10 via a gear transmission coupling assembly, illustrated by reference numeral 44. The rotation of insulator stack I0 is transmitted upward to hinge contact32of the disconnect switch 100 to move contact blade 30 to the open position of 30 as, for example, in the manner shown in U.S. Pat. No. 3,143,608, issued Aug. 4, 1964.

The open position of the disconnect switch I00 shows the blade 30' as having a widened beavertail end 46 and articu' lated with the top of insulator 12 for vertical swinging motion by means of a hinged bearing 48. The hinged bearing 48 includes roller bearings (not shown) to allow rotation of the blade 30 about its longitudinal axis when in closed position. In the closed (i.e. solid line) position when in the drawing, the blade 30 has been swung to the point where its end 34 enters the contact jaw 36. That assembly 36 includes a pair of contact members 50, between which the blade 30 has been rotated so that its beavertail end 46 is wedged between the contact members 50 which then firmly grip the blade.

As thus far described, the disconnect switch of the drawing is quite similar to previously known constructions. However, the switch of the drawing further includes apparatus for reducing its susceptibility to electrical breakdown, corona discharge and radio interference. In particular, the disconnect switch of the drawing further includes a grading post of mast 52, of substantially the same length as contact blade 30, extending in a vertical direction comparable to that of the blade 30 when in the open position 30. (The use of a grading post having a centered spherical projection at the end thereof as a means of minimizing electrical breakdown is known, and need not be described in detail here. As is well appreciated, the grading post effectively controls the voltage of the insulator stack by reducing the gradient on the top unit and distributing the voltage more uniformly over the stack).

Furthermore, the arrangement of the drawing includes a substantially spherical projection 54 affixed to the end of the blade 30 adjacent the beavertail 46. As will also be appreciated, the substantially smooth surface presented by this projection 54, cooperates with the correspondingly smooth surface of the spherical projection 56 of the grading post 42 to effectively reduce corona and radio interference and to keep the energized blade 30 corona-free in the open position. While, in general, this spherical projection arrangement serves to reduce the electric field which exists between the grading post 42 and the contact blade 30 when in open position, there still remains a substantial electric field when voltages of the order of 700 kv. and currents of the order of 3,000 amperes are carried by the switch 100.

However, in accordance with the invention, it has been found that the electric field which exists between the grading post 52 and the contact blade 30 in open position can be reduced still further by offsetting the spherical projection 54 relative to the blade 20, as well as offsetting the projection 56, heretofore centered, with respect to the mast 52. That is, as

' shown in the drawing, the projection 54 is arranged in nonaxial alignment with its contact blade 30, and the projection 56 is similarly arranged in nonalignment with its grading post 52. Also, it will be seen that these projections are so arranged that their separation when the blade 30 is in its open position (30') is greater than the separation between the axis of blade 30 and grading post 52 when correspondingly oriented-that is when extending vertically.

Just as the use of a grading post as a means of reducing electrical breakdown is known so, too, is it known to use an offset spherical projection on the energized contact blade of a disconnect switch. US. Pat. No. 3,288,955, issued Nov. 29, 1966 shows just such an offset configuration. However, the

offset configuration of that U.S. Pat. No. 3,288,955 is selected for mechanical reasons-namely, to improve the fit of the contact blade with the jaw assembly as compared to the fit obtained if the spherical projection on the blade were centered. Also, it will be noted from that patent that no grading post or spherical projection thereon is employed. Combining the disconnect switch of U.S. Pat. No. 3,288,955 with its offset contact blade projection with known grading post projection arrangements has also been found to provide poorer operating characteristics than are provided by the instant invention, since such combined structures continue to employ a grading post having a centered projection.

in prior art constructions both the contact blade and the grading post have centered spherical projections, but a blade rotation of 93 is employed in operating the vertical break switch to achieve satisfactory operation at voltages and currents comparable to those here described. As will readily be appreciated, conventional disconnect switch mechanisms provide rotationsof 90 only and special mechanisms were required to cause rotation beyond that amount. As will also be appreciated, such rotation beyond 90 usually necessitates an increase in the amount of ground space required in disconnect switch constructions for adequate clearance to be had.

With the switch arrangement of the instant invention, on the other hand, where both the spherical projection on the contact blade and the projection on the grading post are offset away from one another, it has been found that only 90 rotation of the energized blade is needed to effect the requisite reduction in electrical field. The need for special mechanisms and increased acreage requirements are, therefore, unnecessary.

The offset projection arrangement of the invention similarly represents an improvement over other centered-projection configurations where comparable results can be obtained by tilting the grading post at an angle with respect to the contact blade when in open position. In this respect, it will be seen that such an angled grading mast might very well be mistaken by maintenance personnel as one constructed in error, not appreciating the need therefor. These personnel may then mistakenly rearrange the post in its usual 90 position and thereby destroy the effect it is designed to produce. Thus, while other arrangements are possible to reduce electrical breakdown with disconnect switches operating at extra high voltages and currents, the switch of the instant invention proves attractive both in its simplicity of design and in its requiring little or no modification of cooperating structures heretofore employed. All that is necessary is to offset a spherical projection both on the contact blade 30 and on the grading post 52 so that their respective separation exceeds that between the blade and post when oriented in a vertical position. The contact blade 30 may then be fitted into a U-bolt or similar such attachment at its end remote from such projection, and mounted in turn by a supporting bracket to the insulator stacks 10, 12.

I claim: 1. An electrical switch having reduced susceptibility to electrical breakdown comprising:

an elongated contact blade pivotally supported at one end for movement to switch-closing and switch-opening positions respectively; contact means including a first substantially spherical projection at the opposite end of said contact blade; a jaw contact positioned for cooperative engagement with said contact means when said contact blade is in said switch-closed position, and for disengagement from said thereof remote from said jaw contact; with said first and second spherical pro ections being offset with respect to their respective contact blade and grading post support members so that their separation is greater than that between said contact blade and said grading post when both are oriented in said vertically extending plane. e I

2. Theelectrical switch of claim 1 wherein said contact blade and said grading post are of substantially the same,

lengths and wherein said grading post and said contactblade in switch-opened position both extend at an angle with respect to the orientation of said contact blade when in said switch-closed position.

3. The electrical switch of claim 1 wherein said elongated contact blade. is pivotally supported for compound angular movement in at least two directions to said switch-closing and said switch-opening positions, and wherein there is further included blade operating means operatively connected to said one end of said elongated contact blade for moving said contact blade in a predeterminedpath between said open and closed positions, said blade operating means including means for moving said contact blade about a vertically extending axis to define movement in a first angular direction and for moving said contact blade about a horizontal axis to define movement in a second angular direction.

4. The electrical switch of claim 3 wherein said contact means further includes a beavertail contact means having a first dimension along a first direction thereof and a second. dimension along a second direction thereof with said second dimension being greater than, said first dimension, wherein said jaw contact is resiliently formed having an opening when in the relaxed condition intermediate said first and second dimension, and wherein said beavertail contact is adapted to enter said jaw opening along said first direction and to turn within said jaw opening upon subsequent rotation of said contact blade for force opening said jaw opening to accommodate said second dimension, whereby firm electrical engagement is maintained between said contact blade and said jaw contact.

5. A switch assembly comprising first and second longitudinally displaced support structures vertically extending upward from a ground plane, first and second insulator stacks secured to the upper ends of respective ones of said support structures and vertically extending upwardly therefrom, jaw contact means positioned at the upper end of said first insulator stack, a disconnect switch having a contact blade pivotally supportedat the upper end of said second insulator stack, said disconnect switch contact arm movable into and out of engagement with said contact jaw means and having a first substantially spherical projection at the end of said contact blade remote from said second insulator stack; and grading post extending in a vertical plane from said jaw contact means having a second substantially spherical projection at the end thereof remote from said jaw contact; with said first and second projections being offset with respect to their contact blade and grading post support members so that their separation is greater than that between said contact blade and said grading post when said members are correspondingly oriented in a vertical plane, within which said contact blade is in its switchopen position. 

1. An electrical switch having reduced susceptibility to electrical breakdown comprising: an elongated contact blade pivotally supported at one end for movement to switch-closing and switch-opening positions respectively; contact means including a first substantially spherical projection at the opposite end of said contact blade; a jaw contact positioned for cooperative engagement with said contact means when said contact blade is in said switch-closed position, and for disengagement from said contact means when said contact blade extends in a vertical plane when said blade is in said switch-opened position; grading post means positioned adjacent said jaw contact and extending in said same vertical plane and having a second substantially spherical projection at the end thereof remote from said jaw contact; with said first and second spherical projections being offset with respect to their respective contact blade and grading post support members so that their separation is greater than that between said contact blade and said grading post when both are oriented in said vertically extending plane.
 2. The electrical switch of claim 1 wherein said contact blade and said grading post are of substantially the same lengths and wherein said grading post and said contact blade in switch-opened position both extend at an angle 90* with respect to the orientation of said contact blade when in said switch-closed position.
 3. The electrical switch of claim 1 wherein said elongated contact blade is pivotally supported for compound angular movement in at least two directions to said switch-closing and said switch-opening positions, and wherein there is further included blade operating means operatively connected to said one end of said elongated contact blade for moving said contact blade in a predetermined path between said open and closed positions, said blade operating means including means for moving said contact blade about a vertically extending axis to define movement in a first angular direction and for moving said contact blade about a horizontal axis to define movement in a second angular direction.
 4. The electrical switch of claim 3 wherein said contact means further includes a beavertail contact means having a first dimension along a first direction thereof and a second dimension along a second direction thereof with said second dimension being greater than said first dimension, wherein said jaw contact is resiliently formed having an opening when in the relaxed condition intermediate said first and second dimension, and wherein said beavertail contact is adapted to enter said jaw opening along said first direction and to turn within said jaw opening upon subsequent rotation of said contact blade for force opening said jaw opening to accommodate said second dimension, whereby firm electrical engagement is maintained between said contact blade and said jaw contact.
 5. A switch assembly comprising first and second longitudinally displaced support structures vertically extending upward from a ground plane, first and second insulator stacks secured to the upper ends of respective ones of said support structures and vertically extending upwardly therefrom, jaw contact means positioned at the upper end of said first insulator stack, a disconnect switch having a contact blade pivotally supported at the upper end of said second insulator stack, said disconnect switch contact arm movable into and out of engagement with said contact jaw means and having a first substantially spherical projection at the end of said contact blade reMote from said second insulator stack; and grading post extending in a vertical plane from said jaw contact means having a second substantially spherical projection at the end thereof remote from said jaw contact; with said first and second projections being offset with respect to their contact blade and grading post support members so that their separation is greater than that between said contact blade and said grading post when said members are correspondingly oriented in a vertical plane, within which said contact blade is in its switch-open position. 